The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Demands for improved performance and fuel economy, as well as reduced cost, waste, and logistical footprints are driving automotive component designs. Recently, multi-material designs have been introduced to leverage the benefits of different materials as desired within a single part. An example is a recent development in the over-molding of structural load-bearing steel inserts with a lighter weight aluminum alloy to produce a compact, lightweight cylinder block (part) that is capable of sustaining increased combustion loading as disclosed in in U.S. Pat. No. 9,086,031, which is commonly assigned with the present application and incorporated herein by reference in its entirety.
In a single material part, geometric features may be produced with a combination of cast features and machined features to deliver the final part design. In the case of over-molded parts, subsequent machining operations may require machining multiple materials or machining a difficult-to-machine material. Continuing with the cylinder block example above, the load-bearing steel insert may be made of a powder forged and sintered material that is difficult to machine and would require a bearing oil feed to be drilled after the casting operation.
Another challenge in the over-molding of inserts is the dimensional tolerances between the insert and the casting mold or tool. Again, citing the cylinder block example above, the steel insert must be retained in the casting mold during the casting process. There will therefore be some regions designed with contact or close-proximity between the steel insert and the casting tool. Due to practical limitations, such as machining variation and dimensional change due to thermal expansion of the insert and/or the casting mold, there may be local areas within the contact regions with no physical contact between the insert and the mold, namely, a gap. Molten alloy can easily flow into this gap and generate a thin layer referred to as flash on the cast part. This flash is shown in FIGS. 1A and 1B, which illustrates a steel insert with a temporary core, an aluminum casting, and flashing from a conventional High Pressure Die Cast (HPDC) process. If the insert surface is geometrically complex, the flash can fully encase a portion of the insert, and removing the flash may be quite difficult without either damaging the insert, the part, or introducing expensive and difficult bi-metallic machining operations.
The present disclosure addresses the challenges of casting multiple parts of different materials within an assembly, among other issues related to casting such assemblies.